PASADENA, Calif. — The most advanced spacecraft to reach Mars has begun adjusting its orbit so that it can study the planet in detail this fall, scientists said Friday.

The Mars Reconnaissance Orbiter fired its thrusters for nearly a minute Thursday to lower its orbit, a step toward the tricky aerobraking process during which the spacecraft will repeatedly dip into the upper atmosphere. The first dip is due next week.

“We have to be sure we don’t dive too deep, because that could overheat parts of the orbiter,” said Daniel Kubitschek of NASA’s Jet Propulsion Laboratory, which is in charge of the $720 million mission.

The unmanned spacecraft will perform 550 such dips over six months. After that, it will begin its two-year science mission mapping the planet, monitoring the atmosphere and scouting for landing sites to send future robotic probes.

The Reconnaissance Orbiter safely entered orbit around Mars on March 10 after a seven-month, 310 million-mile (500 million-kilometer) journey. It joined three other orbiters currently flying around the planet and two rovers rolling across the surface.

Last week, a high-resolution camera aboard the orbiter
beamed back a test image
showing the planet’s southern highlands and cratered surface. Scientists said future pictures from much closer range should capture objects less than 3 feet (1 meter) across.